GPIO

GPIO Functionality and Usage Guide.

Overview

GPIO is the controller for the GPIO module

Functional Description

The Linux GPIO subsystem driver framework mainly consists of three parts:

GPIO Controller Driver: Interacts with the GPIO controller, performing initialization and operations on the controller.
GPIO lib Driver: Provides standard APIs for use by other modules, such as setting GPIO direction and reading/writing GPIO level states.
GPIO Character Device Driver: Exposes GPIOs to user space as character devices, allowing user space to access GPIOs through standard file interfaces.

Source Code Structure

The controller driver code is located in the drivers/gpio directory:

|-- gpio-k1x.c

Key Features

Feature	Description
Direction Configuration Support	Supports setting GPIO as input or output
High/Low Level Output Support	Supports setting the level of GPIO in output mode
GPIO Interrupt Support	Supports GPIO interrupts triggered by rising and falling edge

Configuration Introduction

It mainly includes driver CONFIG enablement configuration and DTS configuration.

CONFIG Configuration

CONFIG_GPIOLIB: Provides support for GPIO controllers, with a Ydefault value of

Device Drivers
        GPIO Support (GPIOLIB [=y])

CONFIG_GPIO_K1X: Provides support for the K1 GPIO controller, with a default value of Y

Device Drivers  
        GPIO Support (GPIOLIB [=y])
                Virtual GPIO drivers  
                        SPACEMIT-K1X GPIO support (GPIO_K1X [=y])

Usage Guide

Using GPIO involves three steps:

GPIO Description
GPIO Pin Configuration
GPIO Usage

Notes:

Pin numbers are defined in the kernel directory include/dt-bindings/pinctrl/k1-x-pinctrl.h.
Pin configuration is the same when a group of pins is set to the GPIO function, meaning that the mux mode, pull-up/pull-down, edge detection, and drive strength configurations are the same.

GPIO Description

Define all GPIOs used in the system.

The gpio-ranges property of the Linux GPIO framework is used for definition. If the pin numbers corresponding to a segment of GPIOs are also consecutive, they are defined as a group.

The GPIO controller definition in the solution DTS file for the example above

&gpio{
        gpio-ranges = <
                &pinctrl 49  GPIO_49  2
                &pinctrl 58  GPIO_58  1
                &pinctrl 63  GPIO_63  5
                &pinctrl 70  PRI_TDI  4
                &pinctrl 74  GPIO_74  1
                &pinctrl 80  GPIO_80  4
                &pinctrl 90  GPIO_90  3
                &pinctrl 96  DVL0     2
                &pinctrl 110 GPIO_110 1
                &pinctrl 114 GPIO_114 3
                &pinctrl 123 GPIO_123 5
        >;
};

GPIO Pin Configuration

Set the pins corresponding to the GPIOs used in the solution to the GPIO function and configure them (edge detection/pull-up/pull-down/drive strength).

Use the pinctrl-single,gpio-range property for setting. If there is a continuous range of pin numbers with the same configuration, they are configured as a group.

Refer to Section Pin Configuration Parameters for pin configuration parameters.

For example:

&pinctrl {
        pinctrl-single,gpio-range = <
                &range GPIO_49  2 (MUX_MODE0 | EDGE_NONE | PULL_UP   | PAD_3V_DS4)
                &range GPIO_58  1 (MUX_MODE0 | EDGE_NONE | PULL_DOWN | PAD_1V8_DS2)
                &range GPIO_63  2 (MUX_MODE0 | EDGE_NONE | PULL_DOWN | PAD_1V8_DS2)
                &range GPIO_65  1 (MUX_MODE0 | EDGE_NONE | PULL_UP   | PAD_1V8_DS2)
                &range GPIO_66  2 (MUX_MODE0 | EDGE_NONE | PULL_UP   | PAD_3V_DS4)
                &range PRI_TDI  2 (MUX_MODE1 | EDGE_NONE | PULL_UP   | PAD_1V8_DS2)
                &range PRI_TCK  1 (MUX_MODE1 | EDGE_NONE | PULL_DOWN | PAD_1V8_DS2)
                &range PRI_TDO  1 (MUX_MODE1 | EDGE_NONE | PULL_UP   | PAD_1V8_DS2)
                &range GPIO_74  1 (MUX_MODE0 | EDGE_NONE | PULL_UP   | PAD_1V8_DS2)
                &range GPIO_80  1 (MUX_MODE0 | EDGE_NONE | PULL_UP   | PAD_3V_DS4)
                &range GPIO_81  3 (MUX_MODE0 | EDGE_NONE | PULL_UP   | PAD_1V8_DS2)
                &range GPIO_90  1 (MUX_MODE0 | EDGE_NONE | PULL_DOWN | PAD_1V8_DS2)
                &range GPIO_91  2 (MUX_MODE0 | EDGE_NONE | PULL_UP   | PAD_1V8_DS2)
                &range DVL0     2 (MUX_MODE1 | EDGE_NONE | PULL_DOWN | PAD_1V8_DS2)
                &range GPIO_110 1 (MUX_MODE0 | EDGE_NONE | PULL_DOWN | PAD_1V8_DS2)
                &range GPIO_114 1 (MUX_MODE0 | EDGE_NONE | PULL_DOWN | PAD_1V8_DS2)
                &range GPIO_115 1 (MUX_MODE0 | EDGE_NONE | PULL_DOWN | PAD_1V8_DS2)
                &range GPIO_116 1 (MUX_MODE0 | EDGE_NONE | PULL_UP   | PAD_1V8_DS2)
                &range GPIO_123 1 (MUX_MODE0 | EDGE_NONE | PULL_DOWN | PAD_1V8_DS2)
                &range GPIO_124 1 (MUX_MODE0 | EDGE_NONE | PULL_UP   | PAD_1V8_DS2)
                &range GPIO_125 3 (MUX_MODE0 | EDGE_NONE | PULL_DOWN | PAD_1V8_DS2)
        >;
};

GPIO Usage

For example, in the solution, eth0 uses gpio 110 as the PHY Reset signal:

&eth0 {
    emac,reset-gpio = <&gpio 110 0>;
};

Interface Introduction

API

Request a specified GPIO

int gpio_request(unsigned gpio, const char *label);

Release a specified GPIO that has been requested

void gpio_free(unsigned gpio);

Set a specified GPIO to input mode

int gpio_direction_input(unsigned gpio)

Set a specified GPIO to output mode and assign an initial value

int gpio_direction_output(unsigned gpio, int value)

Set the output value of a specified GPIO

void gpio_set_value(unsigned gpio, int value)

Get the signal value of a specified GPIO

int gpio_get_value(unsigned gpio)

Get the interrupt number corresponding to the specified GPIO.

int gpio_to_irq(unsigned gpio)

Debugging

sysfs

Accessing and Controlling GPIOs via sysfs.

/sys/class/gpio
|-- export
|-- gpiochip0 -> ../../devices/gpiochip0/gpio/gpiochip0
|-- gpiochip512 -> ../../devices/platform/soc/d401d800.i2c/i2c-8/8-0041/spacemit-pinctrl@spm8821/gpio/gpiochip512
`-- unexport

export: Used to inform the system to export the specified GPIO pin number for control
unexport: Used to inform the system to unexport (remove) the GPIO pin
gpiochipX: Detailed information of GPIO chip X
gpioX/direction: Direction setting of GPIO X
gpioX/value: Port value of GPIO X

debugfs

Inspect the system’s GPIO controllers and the GPIO information they manage.

/sys/kernel/debug/gpio
# cat gpio
gpiochip0: GPIOs 0-127, k1x-gpio:
 gpio-63  (                    |reset               ) out lo
 gpio-67  (                    |pwr                 ) out hi
 gpio-80  (                    |cd                  ) in  hi ACTIVE LOW
 gpio-96  (                    |sys-led             ) out lo
 gpio-97  (                    |vbus                ) out hi
 gpio-110 (                    |mdio-reset          ) out hi
 gpio-111 (                    |reset               ) out lo
 gpio-113 (                    |pwdn                ) out lo
 gpio-115 (                    |mdio-reset          ) out hi
 gpio-116 (                    |regon               ) out hi
 gpio-123 (                    |hub                 ) out hi
 gpio-124 (                    |hub                 ) out hi
 gpio-127 (                    |?                   ) out lo

gpiochip1: GPIOs 512-517, parent: platform/spacemit-pinctrl@spm8821, spacemit-pinctrl@spm8821, can sleep:

Testing

You can use devmem to check register values and determine whether the GPIO configuration has taken effect.

devmem reg_addr

Overview​

Functional Description​

Source Code Structure​

Key Features​

Configuration Introduction​

CONFIG Configuration​

Usage Guide​

GPIO Description​

GPIO Pin Configuration​

GPIO Usage​

Interface Introduction​

API​

Debugging​

sysfs​

debugfs​

Testing​

FAQ​